How to get the value of the matrix socket via scriptsNode
When creating a subprogram in Animation Nodes (eg. Script Node), you are only defining what that subprogram do, in order to actually use it, you have to Invoke the subprogram. You can invoke a subprogram by adding an Invoke Subprogram Node pointing to the required subprogram, this can be done through the Subprograms panel in the Add Node menu where all subprograms are listed:



To get the value of some data in the script, you add an input with the same type, in your case, it is a Matrix List and input the data to it. A variable that carry the input data is automatically created with the name of the input, in our case, it is called MatrixList, you can use this variable to do what ever you want with the input data. For instance, you can print the list and its length as follows: